A rookie NYPD officer was convicted of manslaughter Thursday, the top charge against him, for firing a bullet that ricocheted in the darkened stairwell of a Brooklyn housing project, killing an innocent, unarmed passerby.

Former police officer Peter Liang, who was immediately fired from the force upon the Brooklyn jury’s guilty verdict, now faces as much as 5 to 15 years in prison for the death of 28-year-old Akai Gurley.

He will be sentenced April 14.

Akai Gurley’s girlfriend Melissa Butler (left) was with Gurley in the dark stairwell when he was fatally shot.

Liang, 28, leaned forward at the defense table and put his head in his hands, his face anguished, after the verdict was read aloud by the jury foreman. He will remain free without bail until sentencing.

As Liang continued to hold his head, the victim’s domestic partner, Kimberly Ballinger, who attended each day of the trial, smiled.

The jury, which deliberated just over two days, additionally found Liang guilty of misdemeanor official misconduct for the improper use of his weapon while patrolling the stairwell.

His defense attorneys Rae Koshetz and Robert E. Brown have vowed an appeal.

Gurley, the father of a 3-year-old daughter, died when a single bullet from Liang’s gun caromed off a cinderblock wall of a nearly pitch-black stairwell inside the Louis Pink Houses in East New York.

The bullet pierced Gurley’s heart, killing him in minutes.

Jurors were charged with deciding whether, in pulling his trigger, Liang acted recklessly, or merely negligently, or without any guilt at all.

Testimony highlights included a crying Liang taking the stand in his own defense, to insist that the gun “just went off.” But he notably failed to express remorse for Gurley’s death, despite sobbing at one point as he described finding his body on the stairwell.

Gurley’s girlfriend, Melissa Butler, who was with him as he was shot, tearfully described trying to revive him as Liang and his partner, Shaun Landau, passed by the blood-drenched scene without offering any aid. Landau was granted immunity from prosecution in exchange for his testimony and cooperation in the investigation.

Jurors heard multiple read-backs and, on Thursday afternoon, requested a second and third large whiteboard be wheeled back into the jury room late in the day.

They also took another turn Wednesday of trying out the disgraced officer’s unloaded service gun, each handling the weapon and pulling its trigger, to feel for themselves once more, as they had during testimony, the 11 1/2 pounds of force required to pull the trigger.

Liang has claimed that while his gun was out, his finger was not on the trigger, a blatant violation of NYPD protocol, when it accidentally fired.

Jurors looked worn out as they left Brooklyn Supreme Court.

“Very tough decision,” said juror No. 9, Mike Vargas, 62.

Peter Liang’s service weapon

Vargas had said during jury selection that he has family in law enforcement. Asked how that weighed on his verdict, Vargas said only, “They’re here to protect us.”

Koshetz and Brown, tried to convince jurors that Gurley’s death was not criminal, with Brown calling it a “terrible tragedy, but not a crime.”

Assistant District Attorney Joseph Alexis had countered that the rookie officer instead acted intentionally — perhaps when startled by the sudden noise of Gurley and Butler entering the dark stairwell — when he pulled the trigger.

Liang knew he had done wrong in opening fire on that night, Nov. 20, 2014, Alexis argued. Liang first tried to find his spent shell casing in an attempt to cover up that he’d discharged his weapon, and only called it in once he realized the bullet had hit Gurley and the officer couldn’t “hush” the mistake.

He and ADA Marc Fliedner also argued that Liang, regardless of mental state, was better equipped to perform compressions than Butler–who had no training whatsoever and was being yelled instruction by neighbor Melissa Lopez on the phone with 911.

“Today’s verdict represents justice for Akai Gurley who was totally innocent when he was shot and killed that night,” Brooklyn DA Ken Thompson said.

Brooklyn DA Ken ThompsonPhoto: AP

“This defendant ignored official training that he received as a police officer – specifically never to put his finger on the trigger of his gun unless he was ready to shoot and his reckless actions cost Akai Gurley his life – a life that Peter Liang had sworn to protect.”

Throughout the trial, defense attorneys Rae Koshetz and Robert E. Brown attempted to convince jurors that Liang –- who testified, along with other cops, that they were “fed” answers to the CPR exam during their training at the police academy -– felt unqualified to perform the procedure on a profusely bleeding Gurley, and was doing his duty to “render aid” when he tried to radio in.

Conversely, ADA Alexis argued that the newbie officer tried to cover up the discharge, and only called in the shooting once he realized the bullet had hit Gurley and the officer couldn’t “hush” the mistake.

He and ADA Marc Fliedner also argued that Liang, regardless of mental state, was better equipped to perform compressions than Butler–who had no training whatsoever and was being yelled instruction by neighbor Melissa Lopez on the phone with 911.

What actually happened in the stairwell the night of Nov. 20, 2014, remains murky.

Liang testified that he entered the eighth-floor stairwell landing, heard a sound to his left that “startled him,” and the gun “just went off.”

His partner, Shaun Landau, testified that Liang then re-entered the eight floor hallway, at which point Landau asked him “what the f— happened?”

Liang’s partner, Shaun Landau

Butler tearfully told the court that she saw Gurley turn to his left before the door “slammed” open and she saw the flash of a “muzzle burst” –- which sent the two sprinting down the stairs, until Gurley collapsed on the fifth-floor landing.

Evidence shows the bullet ricocheted off the seventh-floor landing’s cinderblock wall, and pierced Gurley’s heart, ending its fatal journey in his liver.

Jurors listened repeatedly to the audio from Lopez’s 911 call, and recordings of the police radio, during the trial, and asked again to review both during deliberations.

The amount of time the cops actually spent in the eighth-floor hallway after the shot was fired remains unclear. Both Liang and Landau have said under oath they had no idea the bullet had hit a person while they bickered about who should call the sergeant.

Liang maintains they only argued for 35 to 45 seconds before re-entering the stairwell to find the bullet. Landau told the Grand Jury it was four minutes, but backed off that answer under questioning from Brown, instead saying it was a little under a minute a half.

Surveillance footage in the Pink Houses lobby shows the officers entering the lobby at 11:11 p.m.

Lopez called 911 at 11:14 p.m. after Butler appeared, distraught and bloodied, outside her apartment peephole.

Liang is first heard on the 911 recording asking Lopez for the building’s address at 11:17 p.m., three minutes later. He asks again, a minute later, at 11:18.

His first dispatch of “Pink Houses, post one” comes across the radio a minute later, at 11:19.

Gurley’s mother Sylvia Palmer has said before that whether or not the shooting was accident, Liang has “shown no remorse,” and has not apologized to the family for causing her son’s death.

Liang, who was initially represented by Stephen Worth, declined use of PBA attorneys and instead went with Koshetz, a former NYPD deputy commissioner, and Brown — a former NYPD officer.

Brown and Koshetz requested a mistrial the first full day of deliberations, with Koshetz calling ADA Alexis’ closing arguments suggesting Liang wanted to “cover up” the shooting “inflammatory and inappropriate.”

Butler was not present for the verdict, and has not been present for the trial since her emotional testimony.

Gurley left behind a 3-year-old daughter, Akaila, and his domestic partner Kimberly Ballinger. Ballinger, along with Gurley’s aunt Hertencia Petersen have been present for the entirety of the case.

His mother and stepfather Sylvia and Ken Palmer arrived halfway though the trial, flying in from Florida.